In studies on two new strains of human retrovirus, preliminary results suggest that these may comprise a new type of HIV-like virus. One strain (MCP-1) was isolated from lymph nodes of a patient with mycosis fungoides who was admitted to the Medical College of Pennsylvania. Another strain (HIVT) was isolated from the blood of a homosexual AIDS patient who came from Malaysia to Taiwan. These viruses exhibited biological characteristics similar to HIV, but their molecular properties differed from HIV-1 and HIV- 2. Further tests for molecular characterization are in progress. These viruses, as well as prototype HIV-1 and SIV, were also found to replicate and show cytopathic effects on some human B and monocytic cell lines as well as on human T cells. Oncogene studies have involved c-Ki-ras and v-mos. A human embryonal carcinoma cell line was found to be induced to differentiate into neuron-like cells by various treatments including berberine, an alkaloid from a Chinese herbal medicine. This cellular differentiation is accompanied by a down-regulation of expression of the amplified c-Ki-ras2 protooncogene. Further studies on v-mos amplification and expression in helper virus- infected S+L-mink cells revealed that the v-mos protein (P37mos), which was abundant in the cells with an anchorage-independent, suspension culture phenotype, was scarcely produced in the ouabain- selected, anchorage-dependent revertant, despite an ample amount of v-mos mRNA. Thus, mechanisms such as instability, or post- transcriptional modulation, of v-mos mRNA are postulated to explain the observation in revertant cells. Screening of a cDNA library constructed from mRNA of SJL/J mouse reticulum cell neoplasm (RCN) with various probes resulted in isolation of a number of cDNA clones which are being further tested for their ability to hybridize with mRNAs of RCN and normal mouse cells in a differential manner.